Polymer polyols (PMPOs) are used in the preparation of polyurethane foams and elastomers and are extensively used on a commercial scale. Polyurethane foams made from such polymer polyols have a wide variety of uses. The two major types of polyurethane foams are slabstock and molded foam. Polyurethane slabstock foams are used in carpet, furniture and bedding applications. Molded polyurethane foams are used in the automotive industry for a broad range of applications.
Polymer polyols are typically produced by polymerizing one or more ethylenically unsaturated monomers dissolved or dispersed in a prepared polyol in the presence of a free radical catalyst to form a stable dispersion of polymer particles in the polyol. Typically, polymer polyols used to produce polyurethane foams having higher load-bearing properties than those produced from unmodified polyols were prepared using acrylonitrile monomer; however, many of those polymer polyols have undesirably high viscosities.
Polyurethane foams having high load-bearing properties are predominantly produced using polymer polyols that are prepared from a high styrene content monomer mixture (for example, 65 to 75 percent styrene). However, polymer polyols produced from such high styrene monomer mixtures often fail to satisfy the ever more demanding needs of industry, including acceptable viscosity, strict stability requirements and increased load-bearing properties.
Stability and low viscosity of polymer polyols are of increasing importance to polyurethane foam manufacturers due to the development of sophisticated, high speed and large volume equipment and systems for handling, mixing and reacting polyurethane-forming ingredients. Polymer polyols must meet certain minimum polymer particle size requirements to avoid plugging or fouling filters, pumps and other parts of such foam processing equipment in relatively short periods of time.
Numerous attempts have been made to produce polymer polyols that will satisfy the above criteria. In particular, Japanese laid-open patent application, Kokai No. 6-228247, teaches a semibatch process for making a polymer polyol by the sequential addition of oxide monomer and its polymerization followed by addition of vinyl monomers and their polymerization in the same reactor. Although the Japanese laid-open application teaches that removal of the DMC catalyst is not required, it fails to even suggest that the processing steps could be anything other than sequential. Thus, while one skilled in the art might infer from reading Kokai '247 that DMC catalysts do not interfere with free radical polymerization, Kokai '247 provides no guidance concerning whether free radical polymerization interferes with DMC catalysis.
U.S. Pat. No. 5,059,641, issued to Hayes et al., discloses very low viscosity PMPOs having high styrene/acrylonitrile ratios and good stability which are produced with epoxy-modified polyols as dispersants. The epoxy-modified polyol dispersant may be made by one of three methods: (1) adding the epoxy resin internally to the modified polyol, (2) capping or coupling a polyol not containing an epoxy resin with such a resin, or (3) providing the epoxy resin both internally to the polyol and as a cap or coupler. Epoxy-modified polyols having a hydroxyl to epoxy ratio of about 8 or less, made by one of these techniques, are said to be superior dispersants and provide polymer polyols having higher styrene contents, improved stability and viscosity properties.
Numerous patents disclose the continuous and semi-batch preparation of PMPOs, including processes where the base polyol is a DMC-catalyzed polyol having a molecular weight greater than 3500 Da.
It would, however, be advantageous to be able to produce a low viscosity, polymer polyol having a solids content of greater than 40 wt. % from a low molecular weight polyol having a high hydroxyl content that has been produced with a DMC (double metal cyanide) catalyst.